800 Megahertz and Coax

[RadioMarkW]

I have a few questions regarding a moble antenna hook-up. I have read that coax lengths over a few feet severly degrade 800 megahertz pickup. Is this true?

Also would it be true for moble hookups also where 18 feet of cable is required. I have used good quality cable that is supposed to be well sheilded.

And while I am at it does any one have a great all around moble antenna they recommend for a through the roof beehive mount? I am looking for reception mainly in the 400, 800 and 148
megahertz segments.

Thank you,

Mark

 

[N_Jay]

1) Its not the shielding that matters, it is the loss.

2) A quick Google search will give you lots of loss charts.

3) Loss is linear over length, twice the length is twice the loss

4) Higher frequencies have higher losses.

 

[kf4lne]

Check with your local comm shop and see what they can come up with that will be less lossy at 800MHz than the typical coax. Somewhere around here I have some RG58 sized coax that has a foil, braid, foil shield and its supposed to be great for 800MHz.

 

[LarrySC]

Commerical antenna Mfg's like MAXRAD supply a good grade RG-58 for all mobile installations. It's not like the old CB steel wire coated with a copper clad. 18' is the limit. At 800 a 3db gain antenna is back to -0- gain if you exceed 18' Good Luck.

 

[KT4HX]

Hi Mark. Here is a link to a good loss calculator: http://www.ocarc.ca/coax.htm

I personally use the Larsen 150/450/800 antenna. It seems to work very well for me. You can check it out at www.hamradio.com item is NMO150/450/800

Just about everyone has their favorite mobile antenna. The main thing is to keep your coax run as short as you can in the vehicle. This is particularly important the higher you go in frequency. Hope that helps.....

 

[RadioMarkW]

Thank you very much!!

You have all been a great help.

I am looking over my moble setup no to see ways to reduce the coax length.

I am fairly new to all this and am trying to get all the info for the best possable set up!

regards,

mark